In Russian, Czech or Slovak, I have never ever seen or heard it being used in the context of an innocent camp. It just means bad kind of prison and sometimes military barracks - when you want to imply you don't like those military barracks.

I do not know how in German.

you can see it in the German word for concentration camp: KonzentrationsLAGER.

Summer camp? https://ru.m.wikipedia.org/wiki/Летний_лагерь

When лагерь is used by itself, it depends on context - could be a prison/labor camp, kids summer camp, a historical military reference to an army camping on a campaign, or even a refugee camp or a tourist camp. Not that different from English “camp” really.

Russian also borrowed lager bier in “лагер” (without the softening “ь”), whereas Czech and Slovak have native words for it (ležák/ležiak) with a similar (if not greater) complexity in styles to Germany.